Oil Light Problem

Its a 1991 Toyota Celica ST,When I start it up the oil light is off,but when it runs for a minute the oil light comes on and stays on.After it comes on I will rev it up a 1000rpms and it will flash for a second then just stay on after its warm.Theres oil and seems to be pressure because the engine isn't knocking or making any noise.iv allready put 400miles on it and the guy says it has been on for months.is it possable that the sensor,or the pump maybe bad?Thanks for helping!

check to see if you have enough oil.

The oil is good,I know about the ups and downs of Honda,but not the Toyota.The question was,could anyone tell me if these cars have certin problems that I should look for?Does it have oil sensor problems or oil pump problems that happen to many Celicas?Should I be worried that my cars gonna throw a rod in downtown Chicago?It should have started making noise by now if it was the oil pump,but it prrr's like a kitten at the moment.Thanks for any help you could give me.